pale blue dot -carl sagan- 第14部分

All　the　signs　of　life　that　we've　discussed　so　far　are　due　to　paratively　simple　forms　（the　methane　in　the　rumens　of　cows　is　generated　by　bacteria　that　homestead　there）。　Had　your　spacecraft　flown　by　the　Earth　a　hundred　million　years　ago；　in　the　age　of　the　dinosaurs　when　there　were　no　humans　and　no　technology；　you　would　still　have　seen　oxygen　and　ozone；　they　chlorophyll　pigment；　and　far　too　much　methane。　At　present；　though；　your　instruments　are　finding　signs　not　just　of　life；　but　of　high　technology—something　that　couldn't　possibly　have　been　detected　even　a　hundred　years　ago：

You　are　detecting　a　particular　kind　of　radio　wave　emanating　from　Earth。　Radio　waves　don't　necessarily　signify　life　and　intelligence　Many　natural　processes　generate　them。　You've　already　found　radio　emissions　from　other；　apparently　uninhabited　worlds—generated　by　electrons　trapped　in　the　strong　magnetic　fields　of　planets；　by　chaotic　motions　at　the　shock　front　that　separates　these　magnetic　fields　from　the　interplanetary　magnetic　field；　and　by　lightning。　（Radio　〃whistlers〃　usually　sweep　from　high　notes　to　low；　and　then　begin　again。）　Some　of　these　radio　emissions　are　continuous；　some　e　in　repetitive　bursts；　some　last　a　few　minutes　and　then　disappear。

But　this　is　different：　A　portion　of　the　radio　transmission　from　Earth　is　at　just　the　frequencies　where　radio　waves　begin　to　leak　out　of　the　planet's　ionosphere；　the　electrically　charged　region　above　the　stratosphere　that　reflects　and　absorbs　radio　waves。　There　is　a　constant　central　frequency　for　each　transmission；　added　to　which　is　a　modulated　signal　（a　plex　sequence　of　ons　and　offs）。　No　electrons　in　magnetic　fields；　no　shock　waves；　no　lightning　discharges　can　generate　something　like　this。　Intelligent　life　seems　to　be　the　only　possible　explanation。　Your　conclusion　that　the　radio　transmission　is　due　to　technology　on　Earth　holds　no　matter　what　the　ons　and　offs　mean：　You　don't　have　to　decode　the　message　to　be　sure　it　is　a　message。　（This　signal　is　really；　let　us　suppose；　munications　from　the　U。S。　Navy　to　its　distant　nuclear…armed　submarines。）

So；　as　an　alien　explorer；　you　would　know　that　at　least　one　species　on　Earth　has　achieved　radio　technology。　Which　one　is　it？　The　beings　that　make　methane？　Those　that　generate　oxygen？　The　ones　whose　pigment　colors　the　landscape　green？　Or　somebody　else；　somebody　more　subtle；　someone　not　otherwise　detectable　to　a　spacecraft　plummeting　by？　To　search　for　this　technological　species；　you　might　want　to　examine　the　Earth　at　finer　and　finer　resolution—seeking；　if　not　the　beings　themselves；　at　least　their　artifacts。

You　look　first　with　a　modest　telescope；　so　the　finest　detail　you　can　resolve　is　one　or　two　kilometers　across。　You　can　make　out　no　monumental　architecture；　no　strange　formations；　no　unnatural　reworking　of　the　landscape；　no　signs　of　life。　You　see　a　dense　atmosphere　in　motion。　The　abundant　water　must　evaporate　and　then　rain　back　down。　Ancient　impact　craters；　apparent　on　the　Earth's　nearby　Moon；　are　almost　wholly　absent。　There　must；　then；　be　a　set　of　processes　whereby　new　land　is　created　and　then　eroded　away　in　much　less　time　than　the　age　of　this　world。　Running　water　is　implicated。　As　you　look　with　finer　and　finer　definition　you　find　mountain　ranges；　river　valleys；　and　many　other　indications　that　the　planet　is　geologically　active。　There　are　also　odd　places　surrounded　by　vegetation；　but　which　are　themselves　denuded　of　plants。　They　look　like　discolored　smudges　on　the　landscape。

When　you　examine　the　Earth　at　about　100…meter　resolution；　everything　changes。　The　planet　is　revealed　to　be　covered　with　straight　lines；　squares；　rectangles；　circles—sometimes　huddling　along　river　banks　or　nestling　on　the　lower　slopes　of　mountains；　sometimes　stretching　over　plains；　but　rarely　in　deserts　or　high　mountains；　and　absolutely　never　in　the　oceans。　Their　regularity；　plexity；　and　distribution　would　be　hard　to　explain　except　by　life　and　intelligence；　although　a　deeper　understanding　of　function　and　purpose　might　be　elusive。　Perhaps　you　would　conclude　only　that　the　dominant　life…forms　have　a　simultaneous　passion　for　territoriality　and　Euclidean　geometry。　At　this　resolution　you　could　not　see　them；　much　less　know　them。

Many　of　the　devegetated　smudges　are　revealed　to　have　an　underlying　checkerboard　geometry。　These　are　the　planets　cities。　Over　much　of　the　landscape；　and　not　just　in　the　cities；　there　is　a　profusion　of　straight　lines；　squares；　rectangles；　circles。　The　dark　smudges　of　the　cities　are　revealed　to　be　highly　geometrized；　with　only　a　few　patches　of　vegetation—themselves　with　highly　regular　boundaries—left　intact。　There　are　occasional　triangles；　and　in　one　city　there　is　even　a　pentagon。

When　you　take　pictures　at　a　meter　resolution　or　better；　you　find　that　the　crisscrossing　straight　lines　within　the　cities　and　the　long　straight　lines　that　join　them　with　other　cities　are　filled　with　streamlined；　multicolored　beings　a　few　meters　in　length；　politely　running　one　behind　the　other；　in　long；　slow　orderly　procession。　They　are　very　patient。　One　stream　of　beings　stops　so　another　stream　can　continue　at　right　angles。　Periodically；　the　favor　is　returned。　At　night；　they　turn　on　two　bright　lights　in　front　so　they　can　see　where　they're　going。　Some；　a　privileged　few；　go　into　little　houses　when　their　workday　is　done　and　retire　for　the　night。　Most　are　homeless　and　sleep　in　the　streets。

At　last！　You've　detected　the　source　of　all　the　technology。　the　dominant　life…forms　on　the　planet。　The　streets　of　the　cities　and　the　roadways　of　the　countryside　are　evidently　built　for　their　benefit。　You　might　believe　that　you　were　really　beginning　to　understand　life　on　Earth。　And　perhaps　you'd　be　right。

If　the　resolution　improved　just　a　little　further；　you'd　discover　tiny　parasites　that　occasionally　enter　and　exit　the　dominant　organisms。　They　play　some　deeper　role；　though；　because　a　stationary　dominant　organism　will　often　start　up　again　just　after　it's　reinfected　by　a　parasite；　and　stop　again　just　before　the　parasite　is　expelled。　This　is　puzzling。　But　no　one　said　life　on　Earth　would　be　easy　to　understand。

All　the　images　you've　taken　so　far　are　in　reflected　sunlight—that　is；　on　the　day　side　of　the　planet。　Something　most　interesting　is　revealed　when　you　photograph　the　Earth　at　light：　The　planet　is　lit　up。　The　brightest　region；　near　the　Arctic　Circle；　is　illuminated　by　the　aurora　borealis—generated　not　by　life　；　but　by　electrons　and　protons　from　the　Sun；　beamed　down　by　the　Earth's　magnetic　field。　Everything　else　you　see　is　due　to　life。　The　lights　recognizably　outline　the　same　continents　you　can　make　out　in　daytime；　and　many　correspond　to　cities　you've　already　mapped。　The　cities　are　concentrated　near　coastlines。　They　tend　to　be　sparser　in　continental　interiors。　Perhaps　the　dominant　organisms　are　desperate　for　seawater　（or　maybe　oceangoing　ships　were　once　essential　for　merce　and　emigration）。

Some　of　the　lights；　though；　are　not　due　to　cities。　In　North　Africa；　the　Middle　East；　and　Siberia；　for　example；　there　are　very　bright　lights　in　a　paratively　barren　landscape　due；　it　turns　out；　to　burnoff　in　oil　and　natural　gas　wells。　In　the　Sea　of　Japan　on　the　day　you　first　look；　there　is　a　strange；　triangular…shaped　area　of　light。　In　daytime　it　corresponds　to　open　ocean。　This　is　no　city。　What　could　it　be？　It　is　in　fact　the　Japanese　squid　fishing　fleet；　using　brilliant　illumination　to　attract　schools　of　squid　up　to　their　deaths。　On　other　days；　this　pattern　of　light　wanders　all　over　the　Pacific　Ocean；　seeking　prey。　In　effect；　what　you　have　discovered　here　is　sushi。

It　seems　sobering　to　me　that　from　space　you　can　so　readily　detect　some　of　the　odds　and　ends　of　life　on　Earth—the　gastrointestinal　habits　of　ruminants；　Japanese　cuisine；　the　means　of　municating　with　nomadic　submarines　that　carry　death　for　200　cities—while　so　much　of　our　monumental　architecture；　our　greatest　engineering　works；　our　efforts　to　care　for　one　another；　are　almost　wholly　invisible。　It's　a　kind　of　parable。



BY　THIS　POINT　your　expedition　to　the　Earth　must　be　considered　highly　successful。　You've　characterized　the　environment；　you've　detected　life；　you've　found　manifestations　of　intelligent　beings；　you　may　even　have　identified　the　dominant　species；　the　one　transfixed　with　geometry　and　rectilinearity。　Surely　this　planet　is　worth　a　longer　and　more　detailed　study。　That's　why　you've　now　inserted　your　spacecraft　into　orbit　around　the　Earth。

Looking　down　on　the　planet；　you　uncover　new　puzzles。　All　over　the　Earth；　smokestacks　are　pouring　carbon　dioxide　and　toxic　chemicals　into　the　air。　So　are　the　dominant　beings　who　run　on　the　roadways。　But　carbon　dioxide　is　a　greenhouse　gas。　As　you　watch；　the　amount　of　it　in　the　atmosphere　increases　steadily；　year　after　year。　The　same　is　true　of　methane　and　other　greenhouse　gases。　If　this　keeps　up；　the　temperature　of　the　planet　is　going　to　increase。　Spectroscopically；　you　discover　another　class　of　molecules　being　injected　into　the　air；　the　chlorofluorocarbons。　Not　only　are　they　greenhouse　gases；　but　they　are　also　devastatingly　effective　in　destroying　the　protective　ozone　layer。

You　look　more　closely　at　the　center　of　the　South　American　continent；　which—as　you　know　by　now—is　a　vast　rain　forest。　Every　night　you　see　thousands　of